1. Field of Invention
The present invention relates in general to a hydraulic braking system and method, and more particularly to a flow control for a hydraulic braking system and method.
2. Description of Related Art
One example of a known braking system of the type indicated above includes (a) a brake cylinder actuated by a pressurized fluid received from a fluid pressure cylinder, (b) a cylinder housing, (c) a pressurizing piston with a large radius portion and a small radius portion fluid-tightly and slidably received within the cylinder housing and cooperating with the cylinder housing to define a front pressurizing chamber and a rear pressurizing chamber, (d) a flow control device provided between the front pressurizing chamber and the rear pressurizing chamber and inhibiting a flow of the fluid from the front pressurizing chamber to the rear pressurizing chamber if a fluid pressure in the front pressurizing chamber is lower than a predetermined value and permitting the flow of the fluid from the front pressurizing chamber to the rear pressurizing chamber if fluid pressure in the front pressurizing chamber is higher than the predetermined value, and (e) a solenoid-operated shut-off valve provided in series with the flow control device and selecting a mode between a mode wherein the flow control device is disabled and a mode wherein the flow control device is enabled.
In this known braking system, if the flow control device is in the “enabled” mode, the flow from the front pressurizing chamber to the rear pressurizing chamber is not permitted while the fluid pressure in the front pressurizing chamber is lower than the predetermined value. If the fluid pressure in the front pressurizing chamber becomes higher than the predetermined value, the flow from the front pressurizing chamber to the rear pressurizing chamber is permitted. For this reason, if the fluid pressure in the front pressurizing chamber is lower than the predetermined value, a first-fill can be done rapidly, because more working fluid is supplied to the brake cylinder than if it is higher at the same stroke rate of the pressurizing piston. Also, in the “disabled” mode, the fluid in the front pressurizing chamber is supplied to the brake cylinder without being supplied to the rear pressurizing chamber.
On the other hand, another example of the known braking system of the type indicated above includes (a) a master cylinder pressurizing a fluid in accordance with an operation of a brake pedal, (b) a brake cylinder actuated by the pressurized fluid received from the master cylinder, (c) a master-cut valve disposed between the master cylinder and the brake cylinder, for selectively permitting and inhibiting a flow of the fluid between the master cylinder and the brake cylinder, and (d) a brake pressure control device provided between the master-cut valve and the brake cylinder, for controlling the fluid pressure in the brake cylinder based upon the operation of said brake pedal.
In this known braking system, if the braking system is in a normal state, the fluid pressure in the brake cylinder is controlled by the brake pressure control device, leaving the master-cut valve shut-off. On the other hand, if the braking system is in an unusual state, the master-cut valve is opened and the fluid pressure in the master cylinder is applied to the brake cylinder to work the brake.
However, if the operation of the brake pedal is unusual there is no way to control the fluid pressure in the brake cylinder by the brake pressure control device.